Mars’ water mystery may have a simple ice answer

Researchers from Rice University used a climate model modified for Mars to explore whether lakes could have survived in places such as Gale Crater near the planet's equator. Their results show that lakes could remain liquid beneath a thin layer of seasonal ice for decades and possibly longer, as long as overall climate conditions remained steady. This finding helps address a long-standing question in Mars research. Geological features shaped by flowing or standing water exist across the planet, yet many climate models indicate early Mars should have been too cold to support liquid water.

The study, published in AGU Advances, offers a new explanation for how lakes could have existed without a warm climate and why ancient Martian lake beds appear so well preserved today.

"Seeing ancient lake basins on Mars without clear evidence of thick, long-lasting ice made me question whether those lakes could have held water for more than a single season in a cold climate," said Eleanor Moreland, a Rice graduate student and lead author of the study. "When our new model began showing lakes that could last for decades with only a thin, seasonally disappearing ice layer, it was exciting that we might finally have a physical mechanism that fits what we see on Mars today."

Turning Earth Climate Tools Toward Mars

To investigate the problem, the team adapted a climate modeling framework known as Proxy System Modeling. The approach was originally developed by Earth climate researcher Sylvia Dee to reconstruct ancient climates using indirect indicators such as tree rings or ice cores.

Mars lacks trees and other familiar climate markers, so the researchers relied instead on data collected by Mars rovers. Rock formations and mineral deposits served as stand-ins for a climate record, allowing the team to infer past conditions.

Over several years, the researchers modified the lake model to reflect Mars as it was about 3.6 billion years ago. They accounted for factors such as weaker sunlight, a carbon dioxide-rich atmosphere, and seasonal differences unique to the planet.

Using the new Lake Modeling on Mars with Atmospheric Reconstructions and Simulations (LakeM2ARS) model, the team ran 64 test scenarios based on measurements from NASA's Curiosity rover in Gale Crater and existing Mars climate simulations.

Each scenario simulated a hypothetical lake inside the crater for 30 Martian years, or about 56 Earth years. This allowed the researchers to test whether lakes could realistically remain liquid under different conditions.

"It was fun to work through the thought experiment of how a lake model designed for Earth could be adapted for another planet, though this process came with a hefty amount of debugging when we had to change, say, gravity," said Dee, an associate professor of Earth, environmental and planetary sciences and co-author of the study.

"We were surprised and encouraged by how sensitively the model responded to parameters like atmospheric pressure and temperature seasonality. It shows that with some creativity and experimentation, Earth-origin models can yield realistic climate scenarios for Mars."

Thin Ice as a Natural Insulator

The simulations produced different outcomes depending on the conditions. In some cases, lakes froze solid during colder seasons. In others, the water stayed liquid beneath a thin ice cover rather than freezing completely.

That thin ice played a crucial role. It acted as an insulating lid, limiting evaporation and water loss while still allowing sunlight to warm the lake during warmer periods of the year.

Because of this seasonal cycle, some modeled lakes showed little change in depth over decades. This suggests they could remain stable for long periods even when average air temperatures stayed below freezing.

"This seasonal ice cover behaves like a natural blanket for the lake," said Kirsten Siebach, an associate professor of Earth, environmental and planetary sciences and co-author of the study.

It insulates the water in winter while allowing it to melt in summer, Siebach said. "Because the ice is thin and temporary, it would leave little evidence behind, which could explain why rovers have not found clear signs of perennial ice or glaciers on Mars," she said.

Rethinking Water on a Cold Mars

The results suggest that early Mars may have supported long-lasting lakes without requiring consistently warm conditions. This challenges earlier assumptions that surface water on Mars would only be possible during extended warm periods.

If lakes were protected by seasonal ice rather than buried under thick permanent ice, many puzzling features on Mars become easier to explain. Preserved shorelines, layered sediments, and mineral deposits may all reflect stable lakes that endured despite a cold climate.

What This Means for Future Mars Research

The researchers plan to apply the LakeM2ARS model to other Martian basins to see whether similar lakes could have existed elsewhere on the planet. They also want to explore how changes in atmospheric composition or groundwater flow may have influenced lake stability over time.

"If similar patterns emerge across the planet, the results would support the idea that even a quite cold early Mars could sustain year-round liquid water, a key ingredient for environments to be suitable for life," Moreland said.

The additional co-authors of this study include Rice undergraduate student Nyla Hartigan, Michael Mischna from the Jet Propulsion Laboratory at the California Institute of Technology, James Russell from Brown University and Grace Bischof and John Moores from York University. The Rice Faculty Initiative Fund and the Canadian Space Agency supported this research.